<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.14/dist/vue.js"></script>
    <title>Document</title>
</head>

<body>
    <div id="app">
        <p>{{count}}</p>
        <p>{{msg}}</p>
        <button @click="add">add</button>
        <p>{{ animal.age }}</p>
    </div>

    <script>
        let app = new Vue({
            el: '#app',
            data() {
                return {
                    count: 0,
                    animal: {
                        name: 'cat',
                        age: 2
                    },
                    msg: 'hello'
                }
            },
            methods: {
                add() {
                    this.count++
                    this.animal.age++
                }
            },
            watch: { // 监听

                count(newVal, oldVal) {
                    if(newVal >= 10) {
                        this.msg = 'hello watch'
                    }
                }


                // count: {
                //     count: true,
                //     // depp: true,
                //     handler(newVal, oldVal) {
                //         console.log(newVal, oldVal);
                //     }
                // }
            }
        })
    </script>
</body>

</html>